Since torches prevent mobs from spawning, is it possible to place enough torches within a specific radius to ensure safety during the night? I'm thinking of a situation without any shelter built, more along the lines of a flat plain. If it is possible, how many torches/how far out do I need to go to make that area safe?

4 Answers
4

Sunlight gives 15 luminance to the blocks it hits directly, or through half steps.

Lava gives 15 luminance.

Lightstone gives 15 luminance.

A jack-o-lantern gives 15 luminance.

A candle gives 14 luminance to the otherwise empty block it occupies.

A redstone candle gives 7 luminance to the otherwise empty block it occupies.

Every tile that isn't a light source has a luminance of one minus the luminance of its neighbors. For example, if you had a 6 and a 4 luminance sources close to each other, attached to a wall, you'd have this distribution:

Every non-glass, non-half step surface in the outer world with 7 or less luminance is eligible for spawning.

Every non-glass, non-half step surface in the Nether is eligible for spawning.

Mob spawners cause mob to spawn at a high rate in any surface within 5 distance of it.

In practice:

Here's what I try to do to ensure a luminance of 7 consistently along a line:

Place the first torch. Pardon my hexadecimal one-sided luminance graph:

EDCBA98765432100000000000000000
↑

Proceed until you find two tiles looking exactly like the next, then go back one.

EDCBA98765432100000000000000000
↑

Plant a torch there. Lo and behold, minimum luminance there will be 8!

EDCBA9889ABCDEDCBA98765432100
↑

GOTO 1

You can adapt this algorithm to your necessities with ease. Just plant a torch in the darkest area when in doubt. (Duh.)

Also:

Put torches directly onto surfaces for best results.

In your mining, be aware that any surface is good enough to spawn...

↓↓↓ ↓↓ All positions marked with an arrow are valid
███ ██↓ spawning points, to the best of my knowledge,
█ █↓ and they all can lead to the just spawned mob
█ █ to reach you.
█ ↓█
█↓↓↓↓↓█ Be vigilant and don't mine caves from the
███████ bottom up :(

The algorithm gives you the least amount of torches you can possibly use to get 8 minimum luminance in a row. That's the bare minimum, and it is useful to know: anything more than that will keep you safe.
–
badp♦Dec 8 '10 at 22:44

I'm interested in what you said about glass and half-steps -- if I build a fortress out of these two materials, I'll be spawn-free even if I miss a torch or two? Also, does that only count half-steps that make a half-block-high surface, or can I stack two half-steps for a clean white floor (or as the step between a half step and a block+half-step step) and remain mob-free?
–
PeterLDec 10 '10 at 1:49

One question, just to confirm - so light from two sources is not additive? I would have thought that the light next to the "4" square would also be "4", from 3 + 1 from the "6".
–
CyclopsDec 29 '10 at 20:17

@cyclops Light is additive in frequency certainly. If you wish to discuss this any further may I suggest physics.stackexchange.com? I unfortunately lack formal education in optics, or human perception thereof ;)
–
badp♦Dec 30 '10 at 16:37

Torches Provide a light level of 14. Note that this is to the block that they are in. Adjacent blocks have a light level of 13. Mobs require a light level of 7 or less to spawn.
This means that mobs can't spawn within 7 of a lit torch. So placing a torch every thirteen tiles will keep a hallway lit.

T____________T
01234567890123

You can expand this to two dimensions by placing a second line of torches 7 to one side and offset by seven.

Torches provide a light of 14, with the light value being reduced by 1 for every tile away.

14 13 12 11 10 9 8 9 10 11 12 13 14

Consider the line of light values above. The 14's are torches. If you put the torches no more than 12 squares away, you will prevent any monster from spawning in a straight line; do note however, that if you go with a strictly grid based system, you will have dark "centers" made from the torch squares. I recommend a staggered grid, each line "shifted" 6 squares from the other, so that the light values prevent the centers from getting to dark.

I'm looking for a way to make sure that no mobs will exist anywhere in my vicinity by just using torches. If I just stand still with a circle of torches with a radius of 11, will it prevent mobs from walking into the area, or to an extent towards me?
–
Nick HDec 8 '10 at 21:10

3

@Nick - No. Light (aside from sunlight) only affects mob spawning. Once the mob spawns, it can happily move into the light. You have to prevent spawning in the first place.
–
sjohnstonDec 8 '10 at 21:21